1. Field of the Invention
This invention relates to medical devices and, in particular, to prostheses for placement in a body lumen.
2. Description of Related Art
The functional vessels of human and animal bodies such as the esophagus, bile duct, and blood vessels occasionally become damaged or diseased. For example, the aortic wall can weaken, resulting in an aneurysm. Upon further exposure to haemodynamic forces, an aneurysm can rupture.
Intraluminal prostheses, such as stents and stent grafts, may be used for treating damaged or diseased functional vessels. For example, a stent graft may be used for repairing abdominal and thoracic aortic aneurysms. Such a stent graft is placed inside the vessel and provides some or all of the functionality of the original, healthy vessel.
One of the challenges of designing and using an intraluminal prosthesis is preventing migration of the prosthesis once it is placed in a body lumen. This challenge is particularly great when the environment in which the prosthesis is placed is subject to a continuous strain, such as by the pulsatile force of blood flow in the vasculature. When an intraluminal prosthesis is used, for example, to repair an aneurysm, migration of the device may result in inadequate exclusion of the aneurysm, and increased risk of aneurysm rupture.
Various devices have been proposed to address migration. For example, a prosthesis may comprise one or more barbs or hooks that extend outwardly from the prosthesis and are configured to engage surrounding body tissue. Typically, such barbs or hooks may be attached to the prosthesis, for example, by sewing, gluing, wrapping, chemical bonding, welding, brazing, soldering, and the like.
Although each of these attachment methods may create a strong bond between the barb and the prosthesis, these bonds have been known to break when the device is placed in situ. One possible explanation is that the attachment is particularly prone to the mechanical and chemical hazards of the intraluminal environment. For example, cardiovascular pulsatile forces may be concentrated at the junction between the barb and the stent, which may also be the site of a weld, solder, or the like. In addition, the saline, oxygen-rich, and acidic physiological environment of the body may tend to weaken and corrode the stent-barb attachment.
One solution to address barb detachment was disclosed in U.S. Pat. No. 5,720,776 to Chuter et al. The barb includes both a mechanical attachment, as well as the traditional solder bond. The mechanical attachment comprises a helical winding of the base of the barb around a strut of the stent. This mechanical attachment supplements the traditional solder bond to help protect the solder joint from breaking. In addition, the barb is made laterally flexible to help accommodate forces acting at the anchor point. These improvements help ensure that the barb does not readily separate from the stent due to a failure of the solder joint alone. While the combination of both solder and a mechanical means to affix the barb to the stent has proved effective in most respects, this area of the barb remains most subject to stresses, such as from cyclic load resulting from the pulsatile action of the implant vessel.